.ac{
    width:100px;
    height:100px;
    background:red;
    position:absolute;
    left:0;
    top:0;
    cursor:pointer;
}
.active{
    background:red;
    color:#fff;
}
.tab{
    width:320px;
    height:280px;
}
.tab div{
    width:320px;
    height:280px;
    border:1px solid #000;
}